The present disclosure relates to an image forming apparatus, particularly an image forming apparatus provided with an electric charge roller (a charge roller) electric-charging an image carrier and a cleaning brush cleaning a surface of the charge roller.
An image forming apparatus often uses a charge roller in order to electrically charge a photosensitive drum as an image carrier. With the object of removing a toner (a developer) and an external additive added to the toner adhered on a surface of the charge roller, a cleaning member comes into contact with the charge roller. Generally, as the charge roller, a cleaning brush is used so that a tip (a top end) of the brush part cleans the surface of the charge roller.
As the cleaning brush increased cleaning performance, a brush roller (a cleaning brush) is well-known to prevent bristles from falling and to keep stable cleaning capacity by weave straight brush yarn (the brush part) and half arc-formed brush yarn into a common base fabric.
Moreover, an image forming apparatus is well-known to stabilize following rotation of the cleaning roller and to keep the cleaning performance for a long time by bringing a cleaning roller (the cleaning brush) with a planted bristle brush or the like contact with the charge roller in a low pressure load.
Furthermore, in the image forming apparatus, generally, the charge roller is made come into contact with the photosensitive drum so that the charge roller rotates following the photosensitive drum by rubber performance of the charge roller. On the other hand, in order to response recent requests of high speed and high definition, a way of decreasing electric discharge irregularity of the charge roller is proposed.
FIG. 8 is a schematic diagram schematically showing a photosensitive drum and a charge roller and the periphery in an image forming apparatus possible to decrease electric discharge irregularity of the charge roller. The image forming apparatus includes, as shown in FIG. 8, a photosensitive drum 101, a charge roller 102, a cleaning blade 103 and a cleaning brush 104. The charge roller 102 electrically charges the photosensitive drum 101. The cleaning blade 103 removes a toner and an external additive 110 adhered on a surface of the photosensitive drum 101. The cleaning brush 104 cleans a surface of the charge roller 102.
The surface of the charge roller 102 has electrical conduction and is formed in a slight rugged shape, that is, with slight protrusions and depressions (refer to FIG. 9). Thereby, a lot of slight gaps are arranged in an area S of the charge roller 102 contacted with the photosensitive drum 101. Therefore, electric discharge is caused in upper stream side and lower stream side of the area S in the rotating direction of the charge roller 102, and moreover, local electric discharge is caused in the area S. As a result, the discharged area is increased and the electric discharge irregularity of the charge roller 102 is decreased. Protrusions 102a on the surface of the charge roller 102 are, as shown in FIG. 9, rounded so as not to damage the surface of the photosensitive drum 101.
In the image forming apparatus, as shown in FIG. 8, the toner and external additive 110 adhered on the surface of the photosensitive drum 101 are removed by the cleaning blade 103. Then, a part of the toner and external additive 110 pass through the cleaning blade 103 and adhere on the surface of the charge roller 102. The toner and external additive 110 adhered on the surface of the charge roller 102 are removed by tips (top ends) of the cleaning brush 104.
However, in the image forming apparatus as shown in FIG. 8, slight protrusions and depressions are formed on the surface of the charge roller 102. Therefore, as shown in FIG. 10, even if tips (top ends) of the cleaning brush 104 comes into contact with the protrusions 102a of the surface of the charge roller 102, they moves to the depressions 102b. That is, the cleaning brush 104 is difficult to contact with the protrusions 102a of the surface of the charge roller 102. As a result, although the toner and external additive 110 adhered on the depressions 102b are removed, it is difficult to remove the toner and external additive 110 adhered on the protrusions 102a. 
Thus, if the protrusions 102a numerously formed on the surface of the charge roller 102 are insufficiently cleaned, the toner and external additive 110 are deposited, and then, the deposits cause variation of resistance to effect a black spot on an image. Because the surface of the charge roller 102 has lots of protrusions 102a, if, corresponding to the protrusions 102a, the black spots are caused, the image entirely becomes dark as a fog image.
Moreover, if the above-mentioned cleaning brush is used, because tips (top ends) of the cleaning brush move to the depressions of the charge roller 102, the protrusions 102a are insufficiently cleaned.